In 1947, Lack was selected to be the first concertmaster of the prestigious Little Orchestra Society of New York, a position she held for two seasons. That year, Lack began performing solos weekly that were broadcast to a national audience over the Mutual radio network. In 1951 she entered the Queen Elisabeth Music Competition in Brussels, Belgium. Despite the fact that both American finalists were given scores of 0 by the Soviet judge in the final round, Fredell Lack came away with a bronze medal and the Prize of Liège.

Also in 1951, Lack moved to Houston, Texas, where her husband had been offered a professorship. About a year later, she suffered what could have been a major setback to her career when a dog bit off the tip of the little finger of her left hand. However, following a year of focused rehabilitation and relearning of technique, she was able to continue performing.

Lack and three principal string players from the Houston Symphony formed the Lyric Art Quartet in 1955 and began several chamber music series around Houston. She began a highly successful Young Audiences program in Houston, which brings classical music to schoolchildren. In 1979, that organization gave to Lack its first in an annual series of awards, and the honor was thenceforth named the "Fredell Lack Award."

In 1959, Fredell Lack began teaching violin at the University of Houston, where she remained on the faculty for 50 years before retiring in 2009. She was the 1982–83 recipient of the Esther Farfel Award, given by colleagues to a single University of Houston faculty member each year. The Texas Music Teachers Association awarded her the Outstanding Teaching Achievement Award (Collegiate), a statewide distinction, in 1990. In 1997, the University of Houston Moores School of Music presented Lack with a Lifetime Achievement Award. In 2007, TexASTA, the Texas division of the American String Teachers Association, presented Lack with the Phyllis Young Outstanding Studio Teacher of the Year Award. Lack also maintains a private studio outside the school. A great many of her students have gone on to musical careers as professional performers and teachers, and a number have become successful solo concert artists. One of Lack's former students, Frank Huang, won the top prize at the highly prestigious Naumburg Competition in 2003, has performed with major orchestras, and has made a critically acclaimed recording debut on Naxos Records. Lack students David Mazzeo, Pálína Árnadóttir, Joyce Hammann, Mariko Inaba, Anabel Ramirez, Gloria Justen, Sharman Plesner, William Pu, Gregory Ewer, Beverly Shin, Maurice Sklar, Martin Valdeschack, Chuong Vu, and Zuo Jun are among others who have had successful concert careers. Lack has also taught numerous sessions at the Meadowmount School of Music, an annual summer program in Upstate New York that was founded and for many years was directed by Lack's former mentor Ivan Galamian.

Fredell Lack was married to Ralph Eichhorn, a gastroenterologist, from 1947 until his death in 2014.[1] She does not use her married name, Eichhorn, professionally. Lack has a daughter, a son, and several grandchildren. She is an active advocate for animal welfare.

Horvit: "Aleinu"; Fantasy ("The Daughters of Jerusalem") for Violin and Orchestra. With University of Houston Moores School of Music Chorale and Symphony Orchestra. Albany Troy 265 CD. (1997). The Fantasy was dedicated to Lack, who premiered the work in 1996.[2]